If the user is authenticated through passport, the request will continue to the requested page. Otherwise the requested path will be saved to req.session.redirect and the user will be redirected to /login. If you want to forward the user to a different page, you could add another route like this:

app.get('/login', function(req, res) {
res.redirect('/auth');
});

After the login, the user can be forwarded to the originally requested page using the saved path in req.session.redirect.